MEMS device with tiltable structure and improved control

Abstract

A MEMS device includes a semiconductor body with a cavity and forming an anchor portion, a tiltable structure elastically suspended over the cavity, first and second support arms to support the tiltable structure, and first and second piezoelectric actuation structures biasable to deform mechanically, generating a rotation of the tiltable structure around a rotation axis. The piezoelectric actuation structures carry first and second piezoelectric displacement sensors. When the tiltable structure rotates around the rotation axis, the displacement sensors are subject to respective mechanical deformations and generate respective sensing signals in phase opposition to each other, indicative of the rotation of the tiltable structure. The sensing signals are configured to be acquired in a differential manner.

The invention claimed is: 
     
       1. A MEMS device, comprising:
 a semiconductor body defining a cavity and forming an anchor portion; 
 a tiltable structure elastically suspended over the cavity; 
 first and second support arms extending along a rotation axis of the tiltable structure between the anchor portion and opposite sides of the tiltable structure; and 
 first and second piezoelectric actuation structures facing opposite sides of the first support arm and extending between the anchor portion and part of the MEMS device, wherein said first and second piezoelectric actuation structures are biasable to deform mechanically, thereby generating a rotation of the tiltable structure around the rotation axis; 
 wherein the first and second piezoelectric actuation structures carry first and second displacement sensors of piezoelectric type and being opposite to each other with respect to the rotation axis; 
 wherein, when the tiltable structure rotates around the rotation axis due to actuation of the first and second piezoelectric actuation structures, the first and second displacement sensors are subject to respective mechanical deformations and generate first and second sensing signals in phase opposition to each other and being indicative of the rotation of the tiltable structure around the rotation axis; and 
 wherein the first and second sensing signals are configured to be acquired in a differential manner. 
 
     
     
       2. The MEMS device according to  claim 1 , wherein the part of the MEMS device comprises said opposite sides of the first support arm. 
     
     
       3. The MEMS device according to  claim 1 , wherein the part of the MEMS device comprises the tiltable structure. 
     
     
       4. The MEMS device according to  claim 1 , wherein the first and second displacement sensors are electrically coupled to a differential acquisition module configured to acquire, in a differential manner, the first and second sensing signals and to generate, based upon the first and the second sensing signals, a differential signal indicative of the rotation of the tiltable structure around the rotation axis. 
     
     
       5. The MEMS device according to  claim 4  wherein the differential acquisition module comprises a differential acquisition circuit including:
 a fully-differential amplifier having a positive input, a negative input, a negative output, and a positive output, the positive input being electrically coupled to the first displacement sensor and the negative input being electrically coupled to the second displacement sensor; 
 a first parallel circuit comprising a first feedback resistor and a first feedback capacitor, the first parallel circuit coupled between the positive input and the negative output; and 
 a second parallel circuit comprising a second feedback resistor and a second feedback capacitor, the second parallel circuit coupled between the negative input and the positive output; 
 wherein a differential voltage is generated between the negative output and the positive output in response to rotation of the tiltable structure around the rotation axis due to actuation of the first and second piezoelectric actuation structures, the differential voltage being said differential signal. 
 
     
     
       6. The MEMS device according to  claim 5 , wherein the first and second feedback capacitors are integrated in the semiconductor body. 
     
     
       7. The MEMS device according to  claim 1 ,
 wherein the first and second displacement sensors extend on respective top surfaces of the first and second piezoelectric actuation structures; and 
 wherein each of the first and the second displacement sensors comprises a respective piezoelectric layer interposed, orthogonally to the respective top surface, between a respective top electrode and a respective bottom electrode which is in contact with the respective top surface of the first or the second piezoelectric actuation structures. 
 
     
     
       8. The MEMS device according to  claim 1 ,
 further comprising third and fourth piezoelectric actuation structures which face opposite sides of the second support arm, extend between the anchor portion and said opposite sides of the second support arm or between the anchor portion and the tiltable structure, and are biasable to deform mechanically, thereby generating the rotation of the tiltable structure around the rotation axis; 
 wherein the third and fourth piezoelectric actuation structures carry third and fourth displacement sensors of piezoelectric type, which are opposite to each other with respect to the rotation axis; and 
 wherein, when the tiltable structure rotates around the rotation axis due to actuation of the first, the second, the third and the fourth piezoelectric actuation structures, the first, the second, the third and the fourth displacement sensors are subject to respective mechanical deformations and generate, respectively, the first, the second, a third, and a fourth sensing signals, the third and the fourth sensing signals being in phase opposition to each other and being indicative of the rotation of the tiltable structure around the rotation axis. 
 
     
     
       9. The MEMS device according to  claim 8 , wherein the first and third displacement sensors are electrically connected in series with each other, and wherein the second and the fourth displacement sensors are electrically connected in series with each other. 
     
     
       10. The MEMS device according to  claim 9 ,
 wherein the first and second displacement sensors extend on respective top surfaces of the first and second piezoelectric actuation structures; 
 wherein each of the first and the second displacement sensors comprises a respective piezoelectric layer interposed, orthogonally to the respective top surface, between a respective top electrode and a respective bottom electrode which is in contact with the respective top surface of the first or the second piezoelectric actuation structures; 
 wherein the third and the fourth displacement sensors extend on respective top surfaces of the third and fourth piezoelectric actuation structures; 
 wherein each of the third and the fourth displacement sensors comprises a respective piezoelectric layer interposed, orthogonally to the respective top surface, between a respective top electrode and a respective bottom electrode which is in contact with the respective top surface of the third or fourth piezoelectric actuation structures; and 
 wherein the bottom electrode of the first displacement sensor is electrically coupled to the top electrode of the third displacement sensor, and wherein the bottom electrode of the second displacement sensor is electrically coupled to the top electrode of the fourth displacement sensor. 
 
     
     
       11. The MEMS device according to  claim 9 ,
 wherein the first and second displacement sensors are electrically coupled to a differential acquisition module configured to acquire, in a differential manner, the first and second sensing signals and to generate, based upon the first and the second sensing signals, a differential signal indicative of the rotation of the tiltable structure around the rotation axis; and 
 wherein the first, the second, the third and the fourth displacement sensors are electrically coupled to the differential acquisition module which is configured to acquire, in a differential manner, the sum of the first and the third sensing signals and the sum of the second and the fourth sensing signals and to generate, on the basis of the sum of the first and the third sensing signals and on the basis of the sum of the second and the fourth sensing signals, said differential signal. 
 
     
     
       12. The MEMS device according to  claim 10 ,
 wherein the first and second displacement sensors are electrically coupled to a differential acquisition module configured to acquire, in a differential manner, the first and second sensing signals and to generate, based upon the first and the second sensing signals, a differential signal indicative of the rotation of the tiltable structure around the rotation axis; and 
 wherein the first, the second, the third and the fourth displacement sensors are electrically coupled to the differential acquisition module which is configured to acquire, in a differential manner, the sum of the first and the third sensing signals and the sum of the second and the fourth sensing signals and to generate, on the basis of the sum of the first and the third sensing signals and on the basis of the sum of the second and the fourth sensing signals, said differential signal. 
 
     
     
       13. The MEMS device according to  claim 1 ,
 wherein the first and the second piezoelectric actuation structures comprise first and second piezoelectric actuator elements of piezoelectric type, which are opposite to each other with respect to the rotation axis; 
 wherein the first displacement sensor and the first piezoelectric actuator element are galvanically insulated from each other; and 
 wherein the second displacement sensor and the second piezoelectric actuator element are galvanically insulated from each other. 
 
     
     
       14. The MEMS device according to  claim 7 ,
 wherein the first and the second piezoelectric actuation structures comprise first and second piezoelectric actuator elements of piezoelectric type, which are opposite to each other with respect to the rotation axis; 
 wherein the first and the second piezoelectric actuator elements extend on the respective top surfaces of the first and second piezoelectric actuation structures; 
 wherein each of the first and second piezoelectric actuator elements comprises a respective piezoelectric layer interposed, orthogonally to the respective top surface, between a respective top electrode and a respective bottom electrode which is in contact with the respective top surface of the first or, respectively, the second piezoelectric actuation structures; and 
 wherein the bottom electrodes or the top electrodes of the first displacement sensor and the first piezoelectric actuator element are electrically coupled to each other, and wherein the bottom electrodes or the top electrodes of the second displacement sensor and of the second piezoelectric actuator element are electrically coupled to each other. 
 
     
     
       15. The MEMS device according to  claim 1 ,
 wherein the first and the second piezoelectric actuation structures are of resonant type; 
 wherein the tiltable structure has a main extension in a horizontal plane defined by first and second horizontal axes perpendicular to each other, the first horizontal axis being parallel to the rotation axis; 
 wherein the first support arm comprises first and second torsional springs rigid to movements outside the horizontal plane and yielding to torsion around the rotation axis, the first torsional spring being coupled to the tiltable structure, the second torsional spring being coupled to the anchor portion, the first and the second torsional springs being mutually coupled at a first constraint region; and 
 wherein the first and the second piezoelectric actuation structures extend between the anchor portion and the first constraint structure, on the respective opposite sides of the first support arm. 
 
     
     
       16. The MEMS device according to  claim 1 , wherein the first and the second displacement sensors are configured to be biased with a direct common mode voltage. 
     
     
       17. An electronic apparatus comprising a MEMS device with the differential acquisition module according to  claim 4 . 
     
     
       18. The electronic apparatus according to  claim 17 , further comprising a biasing module coupled to the differential acquisition module and to the first and the second piezoelectric actuation structures, the biasing module configured to:
 receive, from the differential acquisition module, a displacement signal correlated to the differential signal; 
 generate, based on the displacement signal, actuation signals; and 
 bias, through the actuation signals, the first and second piezoelectric actuation structures. 
 
     
     
       19. A method of using a MEMS device comprising a semiconductor body defining a cavity and forming an anchor portion, a tiltable structure elastically suspended on the cavity, first and second support arms extending between the anchor portion and opposite sides of the tiltable structure along a rotation axis of the tiltable structure, and first and second piezoelectric actuation structures facing opposite sides of the first support arm, extending between the anchor portion and said opposite sides of the first support arm or between the anchor portion and the tiltable structure and being biasable to deform mechanically to thereby generate a rotation of the tiltable structure around the rotation axis, wherein the first and second piezoelectric actuation structures carry first and second displacement sensors of piezoelectric type and being opposite to each other with respect to the rotation axis, the method comprising:
 biasing the first and the second piezoelectric actuation structures to generate rotation of the tiltable structure around the rotation axis; and 
 acquiring, in a differential manner, first and second sensing signals generated by the first and second displacement sensors. 
 
     
     
       20. The method of  claim 19 , wherein the first and second sensing signals are acquired using a differential acquisition module that generates, based upon the first and the second sensing signals, a differential signal indicative of the rotation of the tiltable structure around the rotation axis. 
     
     
       21. The method of  claim 20 , further comprising, when the tiltable structure rotates around the rotation axis due to actuation of the first and second piezoelectric actuation structures, generating a differential voltage between a negative output and a positive output of a fully-differential amplifier having positive input, a negative input, the negative output, and the positive output, the positive input being electrically coupled to the first displacement sensor and the negative input being electrically coupled to the second displacement sensor.